Interplanetary Planar Magnetic Structures

利用Sakigake太阳风数据和Yohkoh太阳软x射线图像，研究了行星际磁场矢量几乎取平行于某一平面的所有方向的平面磁结构与太阳活跃区域膨胀的相关性。在1993年1月至7月期间，我们可以在Yohkoh软x射线图像中识别出三种典型的平面磁结构与Uchida等人[1992]发现的活动区域膨胀，从这些活动区域日冕的环状结构中，即使在没有任何相当大的耀斑的情况下，也以几到几十公里/秒的速度反复向外膨胀。活跃区域的膨胀预计将在太阳质量损失中发挥重要作用。另一方面，在行星际空间中，并非所有的活动区域都被观测到为平面结构。在16个太阳源与活动区重合的Sakigake观测的太阳风等离子体中，9个具有包括平面结构、高离子密度或两者兼有的非螺旋磁场，其余7个（44%）与平均的螺旋磁场没有显著差异。研究了太阳风中的压力梯度作为平面磁结构的候选原因。在没有体速梯度的5个Sakigake平面磁性结构中，有2个处于压力梯度区，其余的不在压力梯度区。扁平、缠绕的高β等离子体磁通管（Crooker et al., 1996）被重新检验以模拟平面磁结构。为了再现平面磁性结构，需要大量螺旋度小的磁链。磁场方向的变化主要是由于绳索轴方向的变化，而不是由于每根绳索的磁场旋转。

Planar magnetic structures in which interplanetary magnetic field vector takes almost all directions that are parallel to a plane are correlated with EXPANDING ACTIVE REGIONS on the Sun by using Sakigake solar wind data and Yohkoh soft X-ray images of the Sun. During the period from January to July, 1993, we could identify three typical planar magnetic structures with the active region expansions found by Uchida et al. [1992] in the Yohkoh soft X-ray images, from which loop-like structures of active-region corona expand outward repeatedly at speeds of a few to a few tens of km/s even in the absence of any sizable flares. The active region expansions are expected to play an important role in mass loss from the Sun. On the other hand, not all the active regions were observed as planar structures in interplanetary space. In 16 Sakigake observations of solar wind plasma whose solar sources coincided with active regions, 9 had non-spiral magnetic field including planar structures, high ion density or both of them, but the other 7 (44%) exhibited no significant difference from average solar wind with spiral field.Pressure gradient in the solar wind is examined as a candidate cause of planar magnetic structures. In five of Sakigake planar magnetic structures with no bulk-speed gradient, two were in the regions of pressure gradient but the others were not. Flattened, intertwined flux tubes of high-beta plasma (Crooker et al., 1996) are re-examined to model planar magnetic structures. In order to reproduce a planar magnetic structure, a large number of flux ropes with small helicity are required. Variation of field direction is mainly due to variation of orientation of rope axs, rather than to field rotations in each of ropes.